Paleontologists had previously found the fossils of some of these shallow-water fishes. The bones in their fins were sturdier and more complex than in other fish species, perhaps allowing them to pull themselves through plant-filled channels, and they had primitive lungs as well as gills. Paleontologists had also found, in somewhat younger sediments, fossils of fishlike animals that likely spent part of their time on land. Known as early tetrapods (a word referring to their four legs), they had modified front and back fins that resembled primitive legs and other features suited for life out of the water. But paleontologists had not found fossils of the transitional animals between shallow-water fishes and limbed animals.

The team that discovered the new fossil decided to focus on far northern Canada when they noticed in a textbook that the region contained sedimentary rock deposited about 375 million years ago, just when shallow-water fishes were predicted by evolutionary science to be making the transition to land. The team had to travel for hours in planes and helicopters to reach the site, and they could work for just a couple of months each summer before snow began to fall. In their fourth summer of fieldwork they found what they had predicted they would find. In an outcropping of rock on the side of a hill, they uncovered the fossil of a creature that they named Tiktaalik. (The name means “big freshwater fish” in the language of the Inuit of northern Canada.) Tiktaalik still had many

Paleontologists searched this valley in Nunavut, near the Arctic Circle in north central Canada, for fossils when they learned that it contained sedimentary rocks deposited during the period when limbed animals were first starting to live on land. Fossils of Tiktaalik were discovered on the dark outcropping of rock on the right side of this photograph.

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